New vobasinyl-ibogan type bisindole alkaloids from Tabernaemontana corymbosa

Ten vobasinyl-ibogan type bisindole alkaloids, including three new ones, tabercorines A-C (1-3), and a new natural product, 17-acetyl-tabemaecorymbosine A (4), were isolated from the twigs and leaves of Tabernaemontana coymbosa. Their structures were elucidated on the basis of spectroscopic data, and the NMR data of 17-acetyl-tabemaecorymbosine A (4) was assigned and reported for the first time. The absolute configurations of 1-4 were determined by CD exciton chirality method. All new compounds were evaluated for in vitro cytotoxicity against various human cancer cell lines. Compounds 1 and 4 showed significant inhibitory effects with IC50 values comparable to those of cisplatin. (C) 2014 Elsevier B.V. All rights reserved.